Re: KMSAN: uninit-value in batadv_nc_worker

[Dmitry Vyukov]

On Thu, Oct 1, 2020 at 12:29 PM syzbot
<syzbot+da9194708de785081f11@xxxxxxxxxxxxxxxxxxxxxxxxx> wrote:
>
> Hello,
>
> syzbot found the following issue on:
>
> HEAD commit:    5edb1df2 kmsan: drop the _nosanitize string functions
> git tree:       https://github.com/google/kmsan.git master
> console output: https://syzkaller.appspot.com/x/log.txt?x=10cc55a7900000
> kernel config:  https://syzkaller.appspot.com/x/.config?x=4991d22eb136035c
> dashboard link: https://syzkaller.appspot.com/bug?extid=da9194708de785081f11
> compiler:       clang version 10.0.0 (https://github.com/llvm/llvm-project/ c2443155a0fb245c8f17f2c1c72b6ea391e86e81)
>
> Unfortunately, I don't have any reproducer for this issue yet.
>
> IMPORTANT: if you fix the issue, please add the following tag to the commit:
> Reported-by: syzbot+da9194708de785081f11@xxxxxxxxxxxxxxxxxxxxxxxxx

It's somewhat unobvious how this can happen (or not?).

But may be related to:
INFO: rcu detected stall in batadv_nc_worker (3)
https://syzkaller.appspot.com/bug?id=6dba9b6476dd536c17afa799a72f265e448ff820

which happens with low frequency for the past 300 days, 21 stalls in total.

If we imagine the list somehow ends up uninitialized, occasional
infinite loops make perfect sense.



> =====================================================
> BUG: KMSAN: uninit-value in batadv_nc_purge_orig_hash net/batman-adv/network-coding.c:408 [inline]
> BUG: KMSAN: uninit-value in batadv_nc_worker+0x1c0/0x1d70 net/batman-adv/network-coding.c:718
> CPU: 0 PID: 7 Comm: kworker/u4:0 Not tainted 5.9.0-rc4-syzkaller #0
> Hardware name: Google Google Compute Engine/Google Compute Engine, BIOS Google 01/01/2011
> Workqueue: bat_events batadv_nc_worker
> Call Trace:
>  __dump_stack lib/dump_stack.c:77 [inline]
>  dump_stack+0x21c/0x280 lib/dump_stack.c:118
>  kmsan_report+0xf7/0x1e0 mm/kmsan/kmsan_report.c:122
>  __msan_warning+0x58/0xa0 mm/kmsan/kmsan_instr.c:201
>  batadv_nc_purge_orig_hash net/batman-adv/network-coding.c:408 [inline]
>  batadv_nc_worker+0x1c0/0x1d70 net/batman-adv/network-coding.c:718
>  process_one_work+0x1688/0x2140 kernel/workqueue.c:2269
>  worker_thread+0x10bc/0x2730 kernel/workqueue.c:2415
>  kthread+0x551/0x590 kernel/kthread.c:293
>  ret_from_fork+0x1f/0x30 arch/x86/entry/entry_64.S:294
>
> Uninit was created at:
>  kmsan_save_stack_with_flags mm/kmsan/kmsan.c:143 [inline]
>  kmsan_internal_poison_shadow+0x66/0xd0 mm/kmsan/kmsan.c:126
>  kmsan_slab_alloc+0x8a/0xe0 mm/kmsan/kmsan_hooks.c:80
>  slab_alloc_node mm/slub.c:2907 [inline]
>  slab_alloc mm/slub.c:2916 [inline]
>  __kmalloc+0x2bb/0x4b0 mm/slub.c:3982
>  kmalloc_array+0x90/0x140 include/linux/slab.h:594
>  batadv_hash_new+0x129/0x530 net/batman-adv/hash.c:52
>  batadv_originator_init+0x9b/0x370 net/batman-adv/originator.c:211
>  batadv_mesh_init+0x4dc/0x9d0 net/batman-adv/main.c:204
>  batadv_softif_init_late+0x6d8/0xa30 net/batman-adv/soft-interface.c:857
>  register_netdevice+0xbbc/0x37d0 net/core/dev.c:9760
>  __rtnl_newlink net/core/rtnetlink.c:3454 [inline]
>  rtnl_newlink+0x2e77/0x3ed0 net/core/rtnetlink.c:3500
>  rtnetlink_rcv_msg+0x142b/0x18c0 net/core/rtnetlink.c:5563
>  netlink_rcv_skb+0x6d7/0x7e0 net/netlink/af_netlink.c:2470
>  rtnetlink_rcv+0x50/0x60 net/core/rtnetlink.c:5581
>  netlink_unicast_kernel net/netlink/af_netlink.c:1304 [inline]
>  netlink_unicast+0x11c8/0x1490 net/netlink/af_netlink.c:1330
>  netlink_sendmsg+0x173a/0x1840 net/netlink/af_netlink.c:1919
>  sock_sendmsg_nosec net/socket.c:651 [inline]
>  sock_sendmsg net/socket.c:671 [inline]
>  __sys_sendto+0x9dc/0xc80 net/socket.c:1992
>  __do_sys_sendto net/socket.c:2004 [inline]
>  __se_sys_sendto+0x107/0x130 net/socket.c:2000
>  __x64_sys_sendto+0x6e/0x90 net/socket.c:2000
>  do_syscall_64+0x9f/0x140 arch/x86/entry/common.c:48
>  entry_SYSCALL_64_after_hwframe+0x44/0xa9
> =====================================================
>
>
> ---
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